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Three-dimensional distribution of organic matter in coastal-deltaic peat : implications for subsidence and carbon dioxide emissions by human-induced peat oxidation
Human-induced groundwater level lowering in the Holocene coastal-deltaic plain of the Netherlands causes oxidation of peat organic matter, resulting in land subsidence and carbon dioxide (CO2) emissions. Here, a three-dimensional (3D) analysis of the distribution of the remaining peat organic matter is presented, to quantify the potential of this area to further subsidence and CO2 emissions by oxidation. Hereto, we established relations between dry mass ratios of organic matter and sediment in peat formed in different environmental settings. This was combined with a high-resolution 3D geological model of the subsurface of the Netherlands to map the proportions of organic matter, clastic sediment and void space in peat. The 3D model indicates that c. 15 km3 of Holocene peat is embedded in the coastal-deltaic plain subsurface, of which c. 1.5 km3 consists of organic matter, 0.4 km3 of sediment, and 13.1 km3 of void space. During future human-induced oxidation, this peat has a volumetric loss potential of 14.6 km3, responsible for locally 0.4–6.0 m of subsidence, and a CO2 emission of 2.0 Gton. The 3D modelling revealed that the amount of peat organic matter varies considerably between regions. Especially the subsurface of urban areas overlying back-barrier peat were identified as hot-spots accommodating the highest quantities of peat organic matter. The peat in agricultural areas contains less organic matter but is more prone to oxidation than peat underlying urban areas, because in the latter settings anthropogenic brought-up soil restricts oxidation. Future mitigation strategies should therefore focus on restricting peat oxidation in the agricultural areas of the coastal-deltaic plain.
Shuffled Complex-Self Adaptive Hybrid EvoLution (SC-SAHEL) optimization framework
Simplicity and flexibility of meta-heuristic optimization algorithms have attracted lots of attention in the field of optimization. Different optimization methods, however, hold algorithm-specific strengths and limitations, and selecting the best-performing algorithm for a specific problem is a tedious task. We introduce a new hybrid optimization framework, entitled Shuffled Complex-Self Adaptive Hybrid EvoLution (SC-SAHEL), which combines the strengths of different evolutionary algorithms (EAs) in a parallel computing scheme. SC-SAHEL explores performance of different EAs, such as the capability to escape local attractions, speed, convergence, etc., during population evolution as each individual EA suits differently to various response surfaces. The SC-SAHEL algorithm is benchmarked over 29 conceptual test functions, and a real-world hydropower reservoir model case study. Results show that the hybrid SCSAHEL algorithm is rigorous and effective in finding global optimum for a majority of test cases, and that it is computationally efficient in comparison to algorithms with individual EA.
Urban water security : a review
We review the increasing body of research on urban water security. First, we reflect on the four different focuses in water security literature: welfare, equity, sustainability and water-related risks. Second, we make an inventory of the multiple perspectives on urban water security: disciplinary perspectives (e.g. engineering, environmental, public policy, public health), problem-oriented perspectives (e.g. water shortage, flooding, water pollution), goal-oriented perspectives (e.g. better water supply and sanitation, better sewerage and wastewater treatment, safety from flooding, proper urban drainage), integrated-water versus water-integrated perspectives, and policy analytical versus governance perspectives. Third, we take a systems perspective on urban water security, taking the pressure-state-impact-response structure as an analytical framework and link that to the ‘urban water transitions framework’ as proposed by Brown et al. (2009). A systems approach can be helpful to comprehend the complexity of the urban system, including its relation with its (global) environment, and better understand the dynamics of urban water security. Finally, we reflect on work done in the area of urban water security indices.
Fast microplastics identification with stimulated Raman scattering microscopy
The abundance of plastic products in modern society has resulted in a proliferation of small plastic particles called “microplastics” in the global environment. Currently, spectroscopic techniques such as Fourier‐transform infrared and spontaneous (i.e. conventional) Raman spectroscopy are widely employed for the identification of the plastic microparticles, but these are rather time consuming. Stimulated Raman scattering (SRS) microscopy, based on the coherent interaction of 2 different laser beams with vibrational levels in the molecules of the sample, would enable much faster detection and identification of microplastics. Here, we present for the first time an SRS‐based method for identifying 5 different high production‐volume polymer types in microplastics extracted from environmental or consumer product samples. The particles from the extracts were collected on a flat alumina filter, and 6 SRS images were acquired at specifically chosen wavenumbers. Next, we decomposed these spectral data into specific images for the 5 polymers selected for calibration. We tested the approach on an artificial mixture of plastic particles and determined the signal‐to‐noise and level of cross talk for the 5 polymer types. As a proof of principle, we identified polyethylene terephthalate particles extracted from a commercial personal care product, demonstrating also the thousand‐fold higher speed of mapping with SRS compared with conventional Raman. Furthermore, after density separation of a Rhine estuary sediment sample, we scanned 1 cm2 of the filter surface in less than 5 hr and detected and identified 88 microplastics, which corresponds to 12,000 particles per kilogram dry weight. We conclude that SRS can be an efficient method for monitoring microplastics in the environment and potentially many other matrices of interest.
Sand behavior under stress states involving principal stress rotation
The behavior of sands exhibiting both unstable and stable response, in their loose deposited state, under axial-torsional shearing involving continuous principal stress rotation is investigated using the hollow cylinder apparatus. This paper examines the parameters affecting the major principal stress direction attained at instability and/or phase transformation during torsional shearing following anisotropic consolidation. It is shown that constant stress ratio (t/p') lines, including the instability and phase transformation lines, are associated with the same major principal stress rotation with respect to the vertical within a wide range of initial mean effective stresses along the same consolidation stress ratio, Kc. In sands exhibiting instability, smaller principal stress rotations are required for the mobilization of the effective stress ratio at the onset of instability as the initial shear stress level increases (Kc decreases). In sands exhibiting stable response, principal stress rotation at phase transformation increases with increasing dilatancy tendencies. The dependence of the angle of shearing resistance, mobilized at instability (IL), phase transformation (PTL), and failure (FL) lines on principal stress rotation and the intermediate stress parameter, b, is examined to verify whether the mobilized angle of shearing resistance can be considered as a material property. In continuous rotation tests, contrary to fixed principal stress direction and b tests, the angle of shearing resistance at IL can be considered as material property. However, the angle of shearing resistance at PTL depends on b and the direction of the principal stress. Moreover, phase transformation takes place at lower stress ratios as density increases.
Using 14C-dated peat beds for reconstructing subsidence by compression in the Holland coastal plain of the Netherlands
Subsidence in the Holland coastal plain of the Netherlands was reconstructed from the vertical displacement of Holocene peat layers below their reference groundwater levels at the time of peat formation. This quantifies the part of subsidence that is due to compression processes and allows specification of the current state of peat compression in a map. 14C-dating of peat layers found intercalated in the Holocene sequence were used in the reconstruction. This dataset was combined with results from a recent coastal-deltaic plain wide three-dimensional (3D) interpolation of reference palaeo-groundwater levels, at which the intercalated peats are thought to have formed before they were buried, compressed, and vertically displaced. Empiric relations between reconstructed displacement and the thickness of overburden were determined and deployed in a national 3D geological subsurface model to establish a subsidence map with continuous cover of the coastal plain. The resulting maps show compressed peat layers under urbanized areas with 1 to 8 m of natural and anthropogenic overburden have subsided 1 to 5 m below the original level of formation. In the agricultural area of the coastal plain, where overburden is merely decimetres thick, consisting of fluvial flood- and sea-ingression deposits, peat generally experienced less than 1 m subsidence. The reference-level reconstruction method is deployable over large coastal plain areas to reconstruct subsidence caused by postdepositional vertical displacement of intercalated peat layers. It could therefore serve as an alternative approach for methods based on soil mechanics, which require input often not available for coastal plains on regional scales.
Atmosphere – vegetation – soil interactions in a climate change context : impact of changing conditions on engineered transport infrastructure slopes in Europe
In assessing the impact of climate change on infrastructure, it is essential to consider the interactions between the atmosphere, vegetation and the near-surface soil. This paper presents an overview of these processes, focusing on recent advances from the literature and those made by members of COST Action TU1202 – Impacts of climate change on engineered slopes for infrastructure. Climate- and vegetation-driven processes (suction generation, erosion, desiccation cracking, freeze-thaw effects) are expected to change in incidence and severity, which will affect the stability of new and existing infrastructure slopes. This paper identifies the climate- and vegetation-driven processes that are of greatest concern, the suite of known unknowns that require further research, and lists key aspect that should be considered for the design of engineered transport infrastructure slopes in the context of climate change.
Laboratory investigation of the Bruun Rule and beach response to sea level rise
Rising sea levels are expected to cause widespread coastal recession over the course of the next century. In this work, new insight into the response of sandy beaches to sea level rise is obtained through a series of comprehensive experiments using monochromatic and random waves in medium scale laboratory wave flumes. Beach profile development from initially planar profiles, and a 2/3 power law profile, exposed to wave conditions that formed barred or bermed profiles and subsequent profile evolution following rises in water level and the same wave conditions are presented. Experiments assess profile response to a step-change in water level as well as the influence of sediment deposition above the still water level (e.g. overwash). A continuity based profile translation model (PTM) is applied to both idealised and measured shoreface profiles, and is used to predict overwash and deposition volumes above the shoreline. Quantitative agreement with the Bruun Rule (and variants of it) is found for measured shoreline recession for both barred and bermed beach profiles. There is some variability between the profiles at equilibrium at the two different water levels. Under these idealised conditions, deviations between the original Bruun Rule, the modification by Rosati et al. (2013) and the PTM model predictions are of the order of 15% and all these model predictions are within 30% of the observed shoreline recession. Measurements of the recession of individual contour responses, such as the shoreline, may be subject to local profile variability; therefore, a measure of the mean recession of the profile is also obtained by averaging the recession of discrete contours throughout the active profile. The mean recession only requires conservation of volume, not conservation of profile shape, to be consistent with the Bruun Rule concept, and is found to be in better agreement with all three model predictions than the recession measured at the shoreline.
41. Dresdner Wasserbaukolloquium 2018 : Wasserbauwerke im Bestand - Sanierung, Umbau, Ersatzneubau und Rückbau (Dresden, 08. und 09. März 2018)
Risk-based safety standards and safety assessment tools in the Netherlands
The Netherlands has established new safety standards for flood defences since 2017. This paper describes the definition and format of the new standards, as well as the tools that have been developed to carry out the assessments in practice. The assessment itself is a layered approach from coarse to fine, including the possibility to work with a conventional semi-probabilistic approach (with partial safety factors), or to opt for full probabilistic analysis. After describing the main features of the assessment, two examples are given for the failure modes of wave overtopping and slope stability. We conclude by pointing out the main differences between the old and the new assessment, and the advantages and opportunities of the new approach.